In recent years, the public has become increasingly aware of the deteriorating quality of our nation's and the world's water supply. Pollutants, biological and toxic waste and other contaminants are being introduced into water supplies at an ever increasing rate, making such water supplies unfit for drinking and other necessary uses. For example, medical patients with low immunity are now being requested not to drink tap water, and disease and illnesses linked to poor quality drinking water have increased dramatically in recent years. This problem is especially significant outside the United States where water quality has deteriorated to an all time low, with the major source of such contamination primarily being bacterial in nature.
Contaminated water is a concern to industry as well. The semiconductor and pharmaceutical industries, among others, require ultra-pure water for their manufacturing processes. Therefore, a great amount of time, money and effort has been invested in developing systems to purify water. However, the systems that currently exist to purify water are generally too expensive or are not feasible in certain locations.
In addition to cost, all current filtration systems suffer from two recurring problems. The first is bacterial growth in the system. The second is fouling of the system due to overloads of contaminants. Either problem will exacerbate the other and reduce the overall efficiency of the system.
Of the current filtration systems available, reverse osmosis systems are the most common solutions for improving water quality through removal of particulates, dissolved solids and bacteria. Generally, these systems use a sediment removal filter in conjunction with activated carbon and a bacteriostatic membrane coated with oxides and halides of silver placed between the filter and the water outlet. Such a system is described in detail by Nishino in U.S. Pat. No. 3,872,013. The membrane will prevent certain bacteria from leaving the filter and will retard their growth on the surface of the membrane, but will not check bacterial growth on the activated carbon or the ability of bacteria to multiply and produce toxins. Other mechanical filters such as ceramic filter cartridges that filter out bacteria of about one micron in size also are ineffective in retarding bacterial growth as the bacteria are collected on the surface of the filter. If allowed to grow unchecked, the bacteria forms a film or slime on the filter which clogs the filter and further increase bacteria growth. Ceramic filters are required to be frequently cleaned by scraping for this reason.
Another type of biocidal reverse osmosis system is described in detail by Von Medlin in U.S. Pat. No. 5,269,919. Von Medlin teaches the use of a polyiodide resin that releases iodide upon contact with bacteria and viral organisms to combat bacterial growth, and uses granular metal alloys and activated carbon to remove iodides released in the water. If not removed, these iodides would be harmful to human beings. In fact, EPA "Policy on Iodine Disinfection", initially developed in 1973 and reaffirmed in 1982, is that iodine disinfection is for short-term only, whenever iodine-containing species remain in the drinking water.
Von Medlin is also representative of a "two-stage" filtration system that is sometimes employed to purify water. In this type of system two separate filtration stages are utilized. These stages are typically connected in series. However, multiple stages can be connected in parallel and in series or some combination thereof for large industrial applications or where the water to be filtered is heavily contaminated. One stage is typically used as a biocidal treatment unit as discussed above. The other stage(s) typically filter particulates and utilize reverse osmosis filters to remove salts and other dissolved materials from the water.
Another type of biocidal water filter is described in detail by Patrick, et al. in U.S. Pat. No. 5,762,797. Patrick teaches wrapping a microporous core with microporous membranes having a pore size distribution between 5.0 and 0.5.mu. in conjunction with a tightly wound criss-cross wrapping of yarn, all of which may be treated with an antimicrobial agent. This type of filter is very effective at removing virtually all bacteria from water. However, these filters are best used as "finishing" filters for water that is already substantially free of contaminants.
If the water to be filtered is heavily contaminated several problems arise. For example, if a single filter cartridge or one "two-stage" system is employed to filter the water, the filter can quickly become fouled thereby severely restricting water flow. To remedy this problem, additional filters may be installed to create a multiple filter system. Such a system distributes particulate matter among several filters, thereby extending the time period between necessary filter maintenance and adding protection against sudden filter failure. Unfortunately, the creation of a multi-filter system using the filters described above will cause too large of a pressure drop across the system. Furthermore, if filters such as those described by Nishino or Von Medlin are used, the surface area upon which bacteria may multiply is greatly increased. Therefore, by adding extra filters to the system, bacteria contamination of the water to be filtered can actually increase.
It therefore can be seen that a need exists for an inexpensive and safe to use filter cartridge for a water filtration system that can filter particulate matter and large organisms and prevent bacterial and viral growth within the filter media, without releasing life harming toxins that have to be further filtered out and which does not unduly restrict water flow through the system.